Tool holder for the shrink-attachment of tools

ABSTRACT

A tool holder comprising a coupling shaft, a shrink chuck and a central member. The shrink chuck has a head and a base, the head having a tensioning portion with a carrier comprising an axial internal bore. The central member is interposed between the coupling shaft and the base. A surface contour connecting the front and rear diameters of the shrink chuck has at least two portions substantially even relative to a diameter course of the contour at the at least two portions. A first portion is disposed on the head and a second portion is disposed on the base, and a transition is interposed between the head and the base. A chuck diameter of the shrink chuck increases in a substantially discontinuous manner at the transition from the first portion to the second portion so that the head is slimmer than the base.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to German Patent Application No. 20 2005 014 350.2 filed on Sep. 9, 2005.

Field of the Invention

The present invention relates to a tool holder for the shrink-attachment of tools having preferably cylindrical shafts or shanks.

BACKGROUND OF THE INVENTION

Tool holders for holding cylindrical shafts or shanks have been known for a long time.

They are used to hold lathe, drilling, fretting/reaming, grinding and milling/cutting tools and comprise a shrink lining or chuck that has a tensioning portion with an axial internal bore within which the tool shaft can be attached by means of shrinking.

During the shrinkage process, the tensioning portion, the internal bore of which has a slightly smaller internal diameter than the external diameter of the tool shaft, is expanded via the application of heat, preferably by means of an induction coil, and is cooled down again after the tool shaft has been inserted, thereby forming a torque-resistant connection between the tool shaft and the shrink chuck.

Hitherto known designs for such tool holders, as are shown, for example, in DE 199 44 440 C2 and DE 101 14 149 C2, already exhibit very good vibration damping and rotational stability. These tool holders do, however, still run the risk of becoming prone to vibrations especially when used with very high-speed rotating tools, whereby the tool, while being rotated, may perform a more or less precision movement around the longitudinal axis of the tool holder and hence the precision and reproducibility of any workpieces made therewith may be diminished. To ensure nevertheless a high degree of accuracy and reproducibility, such tools must, in consequence, not be used at extreme rotational speeds, and the feed rate and cutting depth must not be selected to be too high either. This approach is not ideal, however, in terms of the quantity of material removed, thus preventing the machine operating time for each manufactured workpiece from being optimized.

However, this kind of tool holder does not just entail drawbacks in the case of rapid-rotation tools. In the case of non-rotating tools, as well, the influence of the workpiece that is to be machined may cause the tool to be deflected out of the tool-holder axis and bring about vibrations that likewise place limits on machining precision.

It is therefore the present invention's object to provide a shrink-attachment type tool holder that is less prone to vibrations and thus enables more material to be removed via machining.

SUMMARY OF THE INVENTION

A tool holder in accordance with the present invention is characterized by a shrink chuck contour course in which the shrink chuck diameter extends, in a discontinuous manner, between a first, front diameter at the shrink chuck head and a second, rear diameter at the shrink chuck base in such a way as to form at least two shrinking lining contour portions. In addition, the transition between the first portion and the second portion, in which the diameter rises discontinuously, defines the transition between the shrink chuck head and base.

Not only does this special shape make the shrink chuck head slimmer than the base, but it also lets the head have much less mass, which might give rise to and intensify vibrations, for example, whenever the tool holder is rotated very fast. Such a tool holder may therefore be operated at much higher rotational speeds than conventional tool holders, with the reduced susceptibility to vibrations making it possible to manufacture workpieces with excellent precision and reproducibility. As a result of the fact that the shrink chuck base is designed to have thicker walls than the head, not only are standardized specifications relating to the tool holder design and resulting from the geometrical structure of the machine/tool holder interface complied with, but, at the same time, the shrink chuck is ensured sufficiently high rigidity as well.

In an advantageous embodiment, the tool shaft carrier has an axial limit stop that serves to determine the tool shaft's axial position within the carrier, i.e., a limit stop which determines the tool shaft's penetration depth into the shrink chuck. In relation to the transition, the axial limit stop is arranged such as to receive the tool shaft completely within the shrink chuck head and such that the tool shaft does not partially project into the shrink chuck base. In other words, the axial limit stop is intended to be placed at the height of the transition or between this and the front end of the shrink chuck head, and it is not supposed to be placed within the region between the transition and the lower end of the shrink chuck base. On the one hand, this special axial configuration of the axial limit stop relative to the transition creates a particularly beneficial ratio between the reduced-mass shrink chuck head and the more rigid shrink chuck base. On the other hand, the shrink chuck head can be heated easily by means, for example, of an induction coil, the geometry of which does not need to be complicated. Furthermore, this approach enables the shrink chuck head to be heated and expanded as evenly as possible because there are similar wall thicknesses throughout the tensioning portion, thus stopping the tensioning portion from unevenly heating up and expanding.

The first portion preferably has a conical contour that runs uniformly between the front end of the shrink chuck head and the transition, and the diameter of this first portion extends towards the transition within an angular range of 1° to 20°, especially 4.5°, relative to the tool holder's longitudinal axis. If the shrink chuck head is lent such a geometrical design, the tool holder is compatible with all conventional shrinkage devices.

At the transition, the extension of the shrink chuck contour diameter can run in a range from abruptly, i.e., 0° in terms of being perpendicular to the tool holder's longitudinal axis, up to 50°. Preference is given to a range from 10° to 40°, with particular preference being given to the transition's extension at 30°.

At the lower end of the shrink chuck base adjacent to the central member of the tool holder, the second portion is preferably adjoined by a third portion which has an essentially cylindrical contour, with the second portion having an essentially conical contour that extends towards the third portion at an angle relative to the longitudinal axis in the range of 1° to 20°, particularly 6° in the case of a tool holder with a hollow shaft coupling, and 8° in the case of a tool holder with a tapered shaft coupling. The contour-related transition between the second and third portions occurs in an essentially constant manner, though discontinuous transitions are possible, too. In this way, the base has a standardized contour adjacent to the central member of the tool holder, whereas the region between the third portion and the transition is, on account of the conical contour, reduced additionally in terms of its wall thickness, thereby further reducing the shrink chuck in terms of its mass. As a result, the tool holder's susceptibility to vibrations is further reduced as well.

Particularly in the case of tool holders that have long shrink chucks, it is advantageous for the shrink chuck region to exhibit a four-section contour course, namely a first portion, a second, essentially cylindrical portion adjoining the transition, followed by a flared third portion, which is in turn adjoined by a fourth, essentially cylindrical portion that adjoins the central member and complies with standardized specifications. The conical contour of the third portion is intended to extend towards the central member at an angle relative to the longitudinal axis of the tool holder in the range of 1° to 20°, especially 6° in the case of a tool holder with a hollow shaft coupling, and 8° in the case of a tool holder with a tapered shaft coupling, with the contour-related transitions between the second and third or the third add fourth portions running in an essentially constant manner, though discontinuous transitions are possible, too. Compared to a three-section contour design, the above four-section contour design permits the shrink chuck base mass to be additionally reduced.

In a preferred embodiment, the second portion has bores into which counter-balancing members, particularly counter-balancing screws, can be inserted, which members are used to make concentricity possible by preventing the tool holder from exhibiting imbalances.

An axial internal bore within the tool holder is advantageously provided for cooling the tool while the workpiece is being machined; this bore supplies a cooling fluid to the tool or to the point where the tool engages with the workpiece. This supply channel preferably has a diameter ranging from 3 mm to 6 mm, thereby still ensuring that the tool holder exhibits sufficiently high rigidity. The cooling fluid supplied through the axial supply channel can be supplied to the point where the tool engages with the workpiece either directly via an axial internal bore through the tool to simultaneously cool the tool from within and/or a plurality of bores is provided in the wall of the shrink chuck head, which bores receive the cooling fluid from the supply channel and guide the fluid next to the tool shaft within the tool holder wall, thus causing the cooling fluid to exit the shrink chuck head next to the tool. Alternatively, the coolant lines can be omitted, too, so as to increase rigidity.

Further characteristics, features and advantages of the present invention will now be explained by describing a preferred exemplary embodiment in conjunction with the figures, wherein

These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal sectional view of a preferred embodiment of a tool holder, and

FIG. 2 contains information to explain the tool holder's dimensions in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as orientated in FIG. 1. However, it is to be understood that the invention may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.

FIG. 1 represents as a longitudinal section a tool holder 1 that comprises a hollow shaft coupling 2, a central member 3 and a shrink chuck 4. The shrink chuck 4 has a shrink chuck base 5, the lower region of which is adjacent to the central member 3, and the shrink chuck 4 also has a shrink chuck head 6. It is very easy to identify the four-part contour course of the shrink chuck 4, which course has a first, conical portion 7, a second cylindrical portion 8, a third, conical portion 9 and a fourth, cylindrical portion 10. These portions 7, 8, 9 and 10 connect the essentially rotationally symmetrical contour course of the shrink chuck 4 starting out from a front diameter D1 of the shrink chuck head 6 and terminating at the rear diameter D4 of the shrink chuck base 5.

The contour course of the tool holder diameter runs in an essentially even manner within the individual portions 7, 8, 9 and 10 and constantly between the portions 8, 9 and 10, with the diameter of the shrink chuck 4 increasing continuously starting out from the front diameter D1 as far as the rear diameter D4 and remaining essentially constant only within the second and fourth portions 8 and 10. The diameter increases discontinuously within the transition region 11, i.e., the contour diameter exhibits a discontinuous course during the transition from the first portion 7 to the second portion 8.

As a result of the transition 11, the shrink chuck base 5 has a much larger wall thickness than the shrink chuck head 6, which makes the shrink chuck head 6 not only look slimmer, but also reduces its mass compared to a shrink chuck head 6 whose contour course runs continuously starting out from the shrink chuck base 5.

These measures lower considerably the susceptibility of the tool holder 1 to vibrations, because less mass is located far away from the attachment point of the tool holder 1 within the machine tool and greater mass is placed close to this attachment point. At the same time, the tool holder 1 shown in FIG. 1 exhibits sufficiently high rigidity and complies in particular with standardized specifications that, for example, define the maximum diameter of the fourth portion 10.

In its front region, the shrink chuck head 6 has a tensioning portion that is characterized by an axial internal bore 12 for receiving the tool shaft. The tool shaft's axial penetration depth into the axial internal bore 12 is determined by an axial limit stop 13 that is designed in the shape of a radial constriction of the internal bore 12. As a result of the axial limit stop 13, the tool shaft is in a gripped state only within the shrink chuck head 6, but not in the shrink chuck base 5, thus simplifying and facilitating the shrinkage process considerably.

Adjoining the axial limit stop 13 is a supply channel 14 that is likewise designed as an axial internal bore and supplies coolant to the tool shaft that has been shrunk within the bore 12. The coolant can be fed to the tool head and workpiece either via a coolant channel guided axially within the tool and/or bores (not shown) can be provided within the shrink chuck head 6, which bores, starting out from the supply channel 14, guide the coolant within the wall of the shrink chuck head 6 past the tool shaft to the front end of the shrink chuck head 6. This may, for instance, be brought about by means of two bores that are arranged mirror-symmetrically relative to the longitudinal axis of the tool holder 1 and which run within the first portion 7 next to the tool shaft inside the wall.

In addition, one or more grooves (not shown) can be provided within the bore 12; designed as depressions, these grooves partially increase the internal diameter of the bore 12.

Once the tool shaft has been shrunk into the bore 12, the bore 12 would consequently not be in direct physical contact with the tool shaft in the region of these grooves, thereby forming cavities in these regions; such cavities beneficially receive any moisture, lubricant etc. adhering to the tool shaft so that hydraulic bearings (or hydromounts), which would impede the complete transmission of torque, could not be formed between the bore 12 and the tool shaft. In this respect, a plurality of grooves that run, for example, parallel to the axis or radially relative thereto is preferably replaced by a spirally shaped groove.

FIG. 2 depicts the tool holder 1 from FIG. 1 again as a longitudinal section, though individual dimensions are defined more precisely. The following tables indicate examples of values for the individual dimensions. These values are all given in mm or in ° for the dimensions

,

and

and are listed as a function of the type of tool holder coupling shaft 2 and the shrink chuck's total length L4.

All dimensional data relate to a lower diameter D4 of the shrink chuck base 5 of 50 mm or 53 mm, which diameter is specified in standards by the choice of machine interface. Accordingly, Tables 1, 2, 3 and 4 only go up to a tool shaft diameter D1 of 16 mm, because, if the tool shaft diameters D1 were larger, such a discontinuous transition 11 would essentially no longer be realizable using standard materials.

To provide rotationally stable tool holders in accordance with the present invention in regard to larger tool shaft diameters D1 as well, i.e., tool holders that have the above-described contour course, for applications in high rotational-speed ranges, it would be necessary to make use of larger interfaces that would permit larger diameters D4 of the fourth portion 10.

The angle data for the dimensions

,

and

depend on the choice of the shrink chuck's total length L4 and on the diameter D4 of the shrink chuck base 5. In consequence, they are constant in each of Tables 1, 2, 3 and 4. TABLE 1 D1 D2 D3 D4 L1 L2 L3 L4 L5 L6 L7 α β γ 6 21 40 53 48.5 60.5 84 104 130 38 162 30 4.5 6 8 21 40 53 48.5 60.5 84 104 130 38 162 30 4.5 6 10 24 40 53 55 65.5 84 104 130 43 162 30 4.5 6 12 24 40 53 55 65.5 84 104 130 48 162 30 4.5 6 14 27 42 53 60.5 70.5 84 104 130 48 162 30 4.5 6 16 27 42 53 60.5 70.5 84 104 130 51 162 30 4.5 6

Table 1 lists dimensional data for a tool holder 1 having a hollow shaft coupling 2 for a first shrink chuck length L4. TABLE 2 D1 D2 D3 D4 L1 L2 L3 L4 L5 L6 L7 α β γ 6 21 40 53 48.5 60.5 114 134 160 38 192 30 4.5 6 8 21 40 53 48.5 60.5 114 134 160 38 192 30 4.5 6 10 24 40 53 55 65.5 114 134 160 43 192 30 4.5 6 12 24 40 53 55 65.5 114 134 160 48 192 30 4.5 6 14 27 42 53 60.5 70.5 114 134 160 48 192 30 4.5 6 16 27 42 53 60.5 70.5 114 134 160 51 192 30 4.5 6

Table 2 lists dimensional data for a tool holder 1 having a hollow shaft coupling 2 for a second shrink chuck length L4. TABLE 3 D1 D2 D3 D4 L1 L2 L3 L4 L5 L6 L7 α β γ 6 21 40 50 48.5 60.5 91 110.9 130 38 198.4 30 4.5 8 8 21 40 50 48.5 60.5 91 110.9 130 38 198.4 30 4.5 8 10 24 40 50 55 65.5 91 110.9 130 43 198.4 30 4.5 8 12 24 40 50 55 65.5 91 110.9 130 48 198.4 30 4.5 8 14 27 42 50 60.5 70.5 91 110.9 130 48 198.4 30 4.5 8 16 27 42 50 60.5 70.5 91 110.9 130 51 198.4 30 4.5 8

Table 3 lists dimensional data for a tool holder 1 having a tapered shaft coupling (not shown) for a first shrink chuck length L4, whereby the shape of the tool holder 1 that has a tapered shaft coupling differs from the shape of a tool holder 1 that has a hollow shaft coupling 2 only in the region of the coupling shaft and central member. TABLE 4 D1 D2 D3 D4 L1 L2 L3 L4 L5 L6 L7 α β γ 6 21 40 50 48.5 60.5 121 140.9 160 38 228.4 30 4.5 8 8 21 40 50 48.5 60.5 121 140.9 160 38 228.4 30 4.5 8 10 24 40 50 55 65.5 121 140.9 160 43 228.4 30 4.5 8 12 24 40 50 55 65.5 121 140.9 160 48 228.4 30 4.5 8 14 27 42 50 60.5 70.5 121 140.9 160 48 228.4 30 4.5 8 16 27 42 50 60.5 70.5 121 140.9 160 51 228.4 30 4.5 8

Table 4 lists dimensional data for a tool holder 1 having a tapered shaft coupling (not shown) for a second shrink chuck length L4.

The above-mentioned data make it apparent that a tool holder 1 in accordance with the present invention is much less prone to vibrations than known tool holders, thereby permitting, inter alia, higher rotational speeds so that the quantity of material that is removed during machining and determined by the tool speed, the tool feed rate and the tool's cutting depth can be increased, thus simultaneously decreasing the machine operating times needed to manufacture a workpiece. Accordingly, a tool holder according to the present invention enables workpieces to be made and machined much more efficiently and with greater economy.

The above description is considered that of the preferred embodiment only. Modification of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiment shown in the drawings and described above is merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents. 

1. A tool holder for shrink-attachment of tools having preferably cylindrical tool shafts, comprising: a coupling shaft for coupling to a machine tool; a shrink chuck having a shrink chuck head and a shrink chuck base, the shrink chuck head having a tensioning portion with a carrier comprising an axial internal bore for gripping the tool shaft; and a central member interposed between the coupling shaft and the shrink chuck base; the shrink chuck having a front diameter at the shrink chuck head for facing towards the machine tool and a rear diameter at the shrink chuck base facing towards the central member; wherein a surface contour connecting the front and rear diameters of the shrink chuck has at least two portions substantially even relative to a diameter course of the contour at the at least two portions, the at least two portions comprising a first portion and a second portion, the first portion being disposed on the shrink chuck head and the second portion being disposed on the shrink chuck base, and a transition being interposed between the shrink chuck head and the shrink chuck base, a chuck diameter of the shrink chuck increasing in a substantially discontinuous manner at the transition from the first portion to the second portion so that the shrink chuck head is slimmer than the shrink chuck base.
 2. A tool holder in accordance with claim 1, wherein: the carrier has an axial limit stop for determining an axial position of the tool shaft within the carrier; and the axial limit stop, when viewed axially, is located at a height or between the position of the transition and a front end of said shrink chuck head so that, in a gripped state relative to the central member, a lower end of the tool shaft, when viewed axially, is located before or at the height of the transition.
 3. A tool holder in accordance with claim 2, wherein: the first portion runs between the front end of the shrink chuck head and the transition, and has a substantially conical periphery.
 4. A tool holder in accordance with claim 3, wherein: a diameter of the periphery extending towards the transition at an angle relative to a longitudinal axis of the tool holder at about 1° to 20°.
 5. A tool holder in accordance with claim 4, wherein: the angle is about 4.5°.
 6. A tool holder in accordance with claim 3, wherein: the diameter of the surface contour of the shrink chuck extends at the transition from the first portion to the second portion towards the shrink chuck base at an angle perpendicular to the tool holder's longitudinal axis at about 0° to 50°.
 7. A tool holder in accordance with claim 6, wherein: the angle is about 10° to 40°.
 8. A tool holder in accordance with claim 7, wherein: the angle is about 30°.
 9. A tool holder in accordance with claim 1, wherein: a third portion is interposed between the central member and the second portion, the third portion having a substantially cylindrical periphery and the diameter of a periphery of the second portion flaring out towards the central member at an angle relative to the tool holder's longitudinal axis at about 1° to 20°, a transition of the surface contour occurring substantially continuously between the second and third portions.
 10. A tool holder in accordance with claim 9, wherein: the angle is about 6° if the tool holder has a hollow shaft coupling.
 11. A tool holder in accordance with claim 9, wherein: the angle is about 8° if the tool holder has a tapered shaft coupling.
 12. A tool holder in accordance with claim 1, wherein: a third portion is interposed between the central member and the second portion and a fourth portion is interposed between the third portion and the central member, the second portion and the fourth portion having substantially cylindrical peripheries and the third portion having a substantially conical periphery, a diameter of the periphery of the third portion extending towards the central member at an angle relative to the tool holder's longitudinal axis at about 1° to 20°, transitions of the surface contour occurring substantially continuously between the second and third portions and between the third and forth portions.
 13. A tool holder in accordance with claim 12, wherein: the angle is about 6° if the tool holder has a hollow shaft coupling.
 14. A tool holder in accordance with claim 12, wherein: the angle is about 8° if the tool holder has a tapered shaft coupling.
 15. A tool holder in accordance with claim 1, wherein: bores for counter-balancing members are provided within the second portion.
 16. A tool holder in accordance with claim 1, wherein: the tool holder includes an axial internal bore as a cooling fluid supply channel, the supply channel having a diameter of about 3 mm to 6 mm. 